From what I've read, Li-ion cells / batteries over time can develop internal threads or filaments (also known as "dendrites" I believe, as with neuro-cells).

Evidently, these microscopic, branch-like structures "grow from the anode toward the cathode during charging, potentially penetrating the separator and causing internal short circuits, fire risks, or premature battery failure." --Argonne National Library and scads of [other links](lithium-ion batteries develop dendrites when charging)

Me, on the one hand I'm typically all-thumbs upon power cell chemistry, but OTOH don't want to burn my place down accidentally. At the moment, I've taken to removing most of my collection of lithium-ion cells (apart from my cellphone battery), and placing them in lined, steel pans. Also, when I charge my cellphone these days, I put it in a steel pan, like in the OP. Just to be sure, you know?

Now, do I think that the risk of such Li-ion "dendrites" in cells escaping their outer, protective casing is high? Absolutely not, under normal conditions. (altho that also comes down to quality of the battery, which might be quite sketchy, depending) Meanwhile, do I think that such a potential fire might be disastrous? You betch your bippy I do! (just look at poorly-made ebike batteries for some examples)

So I'm thinking that both old Li-ion cells and ones which are frequently recharged (as with cellphone batteries), are at a higher-level of risk, FWIW.

Got an opinion on all this..?